Bond-length anomaly in InP_1-xAs_x monolayers on InP(001) studied by extended x-ray absorption fine structure

The bond-length relaxation in InP_1-xAs_x monolayers epitaxially grown by metalorganic vapor-phase epitaxy on an InP(001) substrate has been investigated using the extended x-ray absorption fine structures on the As K edge. The In–As bond lengths in InP_1-xAs_x monolayers were determined over a wide range of As composition x (0.08≪x≪0.80). We find that the In–As bond length R_In–As in InP_1-xAs_x monolayer shows an anomaly at x∼0.5; R_In–As is compressed at x∼0.5, deviating from the linear interpolation between the values in a dilute limit (x≪≪1, As:InP) and the strained InAs monolayer (x=1). The As composition dependence of R_In–As coincides with that observed for As atoms incorporated by a surface As–P exchange reaction. The mechanism of anomalous bond-length variation, associated with the change of local structure from the dilute limit to the strained monolayer, is discussed in terms of the elastic energy confined in a strained heterointerface. © 1997 American Institute of Physics.